1. Field of the Invention
The claimed invention relates to a communication circuit for driving a plurality of devices, or more particularly, to a system and method of transmitting a signal to a plurality of slave devices (e.g., memory devices, etc.) via a communication circuit having a plurality of segments that are substantially equal in length and/or impedance.
2. Description of Related Art
As electronic components become cheaper and more readily available, devices that utilize such components (e.g., wireless telephones, personal digital assistants, etc.) become more prevalent. Furthermore, as electronic devices become more prevalent, and competition increases, efforts are typically undertaken to minimize production costs.
One such method of minimizing costs is to minimize real estate (i.e., minimize the size of the electronic circuits located therein). For example, many electronic circuits include a processor and memory devices. In an effort to minimize real estate (i.e., minimize the circuit size), these components are arranged serially. For example, as shown in FIG. 1., the memory devices 132-138 (i.e., slave devices) are arranged serially with respect to the processor 110 (i.e., master device). The processor 110 them communicates (in parallel) with the plurality of memory devices 132-138 via a bus 120.
A drawback with such an arrangement is that the signal received by certain memory devices appears distorted. This is because each memory device (with the exception of the last memory device) receives both the transmitted signal (i.e., the signal transmitted by the processor 110) and a reflected signal (i.e., a signal reflected from the end of the bus, or reflected from the memory device located at the end of the bus). Thus, the signal received by the last memory device 138 (MN) substantially matches the signal transmitted by the processor 110 (P1) (i.e., the signal is substantially well-behaved), whereas the signals received by the remaining memory devices 132-136 appear slightly distorted. In fact, the closer the memory device is to the processor, the more distorted the signal will appear. This is because the time delay between the transmitted signal and the reflected signal is proportional to the signal distortion. In other words, as the time delay increases, so to does the distortion. Thus, the first memory device 132 (M0), which receives the transmitted signal first and the reflected signal last (i.e., experiences the greatest time delay), will receive a signal that is most distorted.
One method of reducing signal-reflection-distortion is through the use of an external termination circuit (i.e., a termination circuit that is external to the processor and the memory devices). Specifically, as shown in FIG. 1, an external termination circuit 140 is placed at the end of the bus 120 in an effort to reduce, or eliminate signal reflection. FIG. 2 provides one example of such an external termination circuit 140. Specifically, the termination circuit 140 includes a plurality of resistors 242, 244 arranged to create a resistor-divider network. In other words, resistor 242 is used to connect the bus 120 to an input voltage (VDD) and resistor 244 is used to connect the bus 120 to ground. The resistor-divider network operates to dampen the signal propagated over the bus 120, thereby reducing (or eliminating) the reflection thereof (i.e., signal reflection).
Another external termination circuit 140 is illustrated in FIG. 3. Specifically, the external termination circuit 140 includes a resistor 344 and a capacitor 346 arranged to create an RC circuit. Such a circuit (like the resistor-divider network) operates to dampen the signal when it reaches the end of the bus, thereby reducing, or eliminating any reflection of the signal. It should be appreciated that the term “external termination circuit” is used herein to identify a termination circuit that is external to the master/slave devices, and not a termination circuit that may be internal to the master (or slave) device.
The drawbacks of using an external termination circuit, however, is that it increases the electronic circuit's size, expense, and power consumption—all of which are undesirable characteristics. For example, with respect to FIG. 2, power is continuously drawn, and therefore wasted, through the two resistors 242, 244 (i.e., from VDD to ground). Therefore, it would be advantageous to be able to reduce (or substantially eliminate) signal-reflection-distortion without having to use an external termination circuit.